1. Field of the Invention
The present invention relates to a method of forming a thin film poly silicon layer and a method of forming a thin film transistor, and more particularly, to a method of directly forming a thin film poly silicon layer on a substrate instead of crystallizing an amorphous silicon layer by laser annealing after depositing the amorphous silicon layer, and a method of forming a thin film transistor including the method of forming the thin film poly silicon layer.
2. Description of the Prior Art
In recent years, applications of flat display devices are rapidly developed. Electronics, such as televisions, cell phones, mobiles, and refrigerators, are installed with flat display devices. A thin film transistor (TFT) is a kind of semiconductor devices commonly used in the flat display device, such as a liquid crystal display (LCD), an organic light emitting diode (OLED) display, and an electronic paper (E-paper).
The thin film transistors in current display industries mainly include amorphous silicon thin film transistors (a-Si TFTs) and poly silicon thin film transistors. The amorphous silicon thin film transistor is currently the mainstream thin film transistor applied in the display industry because of its mature process techniques and high yield. However, the amorphous silicon thin film transistor may not be good enough to satisfy requirements of foreseeable high performance display devices, because the electrical mobility of the amorphous silicon thin film transistor, which is mainly determined by material properties of amorphous silicon, can not be effectively improved by process tuning or design modification. The electrical mobility of the poly silicon thin film transistor is much better because of material properties of poly silicon. In a conventional method of forming a thin film poly silicon layer, an amorphous silicon layer is formed and a thin film poly silicon layer may be obtained after crystallizing the amorphous silicon layer by high temperature or high energy treatments such as laser annealing. However, the crystallization process after the film deposition has several disadvantages such as longer process time, higher cost, and lower manufacturing efficiency. In addition, the uniformity of the crystallization process on a large size substrate is still a problem needed to be solved, and the conventional method of forming the thin film poly silicon layer is accordingly limited to specific products and applications.